Technical Abstract:
Isoxaflutole is a relatively new pre-emergence herbicide used in corn production. Isoxaflutole’s phytotoxic metabolite (DKN) has a low sorption coefficient and may be persistent in soil. This indicates that this herbicide may have a tendency to contaminate water resources through leaching and runoff. Two-year field dissipation studies were conducted in three soil types (sandy loam, loam, and clay loam) in Minnesota (USA) to determine the rate at which isoxaflutole/DKN dissipates under relatively cool, wet soil conditions. Separate plots were treated with isoxaflutole and potassium bromide, a non-sorbed and non-degraded tracer. Soil cores were collected six times during the growing season to a 1-m depth and sectioned into 0-10, 10-20, 20-40, 40-60, and 60-100 cm increments. Bromide or herbicide concentration was measured in replicate samples at each depth at each sampling time. In the first year of the study, isoxaflutole/DKN dissipated by both degradation and transport in each soil. Some leaching of very low concentrations (ng/g) of isoxaflutole/DKN to depths >40 cm was observed. Persistence was estimated by using the bromide results to account for the influence of transport in reducing herbicide concentrations. The degradation half-life of isoxaflutole/DKN was estimated to be about 5 to 10 d in the top 1 m of each soil. Samples from the second year of the study are being analyzed. These results will provide information for the development of best management practices for this herbicide.